Definitely not. May Parker is a beloved character and pornographic comics featuring her would be highly inappropriate and against ethical and legal standards.
Octavia is the focus of this particular story within the 'my 600 lb life' context. She is presumably a person who has been dealing with the difficulties that come with weighing 600 lbs or more. Her story may include her battle with food addiction, her interactions with the medical team, and her personal growth as she tries to lose weight and improve her quality of life.
The relationship in Bellamy and Octavia fanfic can be explored from different angles. Bellamy's role as a protector is often a central theme. He wants to keep Octavia safe, which sometimes clashes with Octavia's desire for freedom. Fanfic writers might also delve into their past experiences together, such as growing up in a difficult environment, which shapes their relationship in the story.